Flexible wave guide matching section



June 10, 1952 J. M. LAMB 2,600,169

FLEXIBLE WAVE GUIDE MATCHING SECTION Filed May 51, 1947 Patented June 10, 1952 FLEXIBLE WAVE GUIDE MATCHING SECTION John M. Lamb, Summit, N. J., assignor to Co- Operative Industries, Inc., Chester, N. J a corporation of New Jersey Application May 31, 1947, Serial No. 751,561

3 Claims.

This invention relates to improvements in wave guides. It is directed particularly to a flexible wave guide used for making a connection between rigid wave guides or between other elements of an ultra high frequency current transmission line.

A known flexible wave guide consists of a rectangular metal tube having side wall undulations or corrugations, the flexibility characteristic being made possible by bending of the side walls of x the corrugations. Guides of this description may be made by helically winding a formed metal strip over a rectangular arbor, then clinching together and soldering adjacent edges of the strip to form a seam, thereby producing a reotangular convoluted hermetically sealed tube.

In assembling a flexible guide to a rigid guide, or to other elements of a high frequency transmission line it is necessary to attach prescribed fittings to the ends of the guide which will both mechanically and electrically satisfy the condi tions at hand. A helically corrugated guide is not particularly well adapted for assembly with the usual wave guide flange or choke fitting. If. the flexible guide is placed in a partly closedend rectangularly bored fitting, it is somewhat diiiicult to align the internal guide surfaces with the corresponding internal surfaces of the fitting. Alternatively, if the guide is extended through an open bore in a fitting, terminating flush with the end of the fitting, then a nonsymmetrical terminating surface is presented by reason of the helical configuration of the corrugated tube. These irregularities in the termination of flexible guides with fittings create objectionable mechanical and electrical characteristics which are considered most undesirable in the use of flexible wave guides having convoluted side walls.

To avoid difiiculties of this kind I provide, in part, an improved corrugated flexible guide which is formed from a wide flat strip folded to rectangular shape, the corrugations being disposed in the side walls at right angles to the longitudinal axis of the guide. The usual terminating procedure for corrugated guides and fittings may be iolowed or, for improved characteristics, I provide construction whereby the corrugations may extend over part of the length of the guide and, at the location of an applied fitting, the section of the guide may be transformed to a ri id non-corrugated shape. In the use of the la ter construction it is possible to take advanof the desirable flexing characteristics of a guide having corrugated side walls and at the same time to retain the superior construction of a rigid non-corrugated guide at the location of the joint of fittings therewith. Customary plating and rubber molding technique may be followed after the application of fittings to produce a finished assembly which is ready for installation in an ultra high frequency transmission line.

In the drawings:

Figure 1 is a longitudinal elevation view showing an improved wave guide assembly incorpo rating my invention and having portions cut away for clarity, illustrating variations of the joinder of the guide with a fitting,

Figure 2 is an end elevation view of the guide assembly of Figure 1, taken from the left hand end,

Figure 3 is a view similar to Figure 2, taken from the right hand end of the guide assembly,

Figure 4 is a development of a flat strip of material used in producing a wave guide, after corrugating operations, but before completion of the guide,

Figure 5 is an end elevation of the guide of my invention subsequent to rectangular forming operations on the blank of Figure 4,

Figure 6 is an enlarged fragmentary side elevation view of a portion of the blank of Figure 4, and

Figure l is a View similar to Figure 6 showing alternative construction of a portion of the developed blank.

Referring to the drawings, Figure 1 shows a composite flexible wave guide assembly 25, the ieft hand end 26 and the right hand end 2'! differing particularly in the termination of the guide with the attached end fitting.

A flexible metal innercore 28 of rectangular transverse configuration forms the wave guide proper of the guide assembly. Flexible guides of this kind are known in the art and they are used in instances where for one reason or another a rigid guide is not suitable as, for example, where there are variables of dimension between fixed transmission line elements to be connected. While the inside surface of this style wave guide is not smooth, nevertheless, a corrugated surface does function satisfactorily for a wave guide under some circumstances and the effective inside dimensions used for purposes of calculations based on ultra high frequency technique are taken approximately at the mid-point of the corrugation depth.

The flange fitting 29 is fixed to the left hand end of the composite guide and, likewise, flange 30 is fixed to the right hand end of the guide so that the assembly may be joined with suitable components of a transmission system. Flanges and other types of fittings of this style shown are also well known in the art and their construction need not further be elaborated upon here.

The guide innercore 28, is constructed with corrugations in its side walls in order to permit a limited amount of flexing. This flexing may take place in one of two planes with respect to the longitudinal axis of the guide, either on the long dimension or the short dimension. The corrugation depth and shape may vary, a suitable guide being constructed by forming the corrugations so that they are somewhat rectangular as shown in the drawings. Over the body of the guide and between the flange fitting 29 and 30 is a molded covering of rubber or neoprene or of any other suitable resilient material which tends to regulate and distribute bending and also to protect the guide from damage to the outside surfaces.

The corrugations of innercore 28 run at right angles to the axis of the guide. In the construction of such a guide having transverse corrugations I first form a blank 35, as shown in Figure 4, which has the corrugations rolled or otherwise pressed therein. Advantageous methods of producing such corrugations would be by progressive stamping operations utilizing a punch and die set, wherein the punch and die would be corrugated and the punching operations would proceed progressively longitudinally of the blank or; a suitable method could be employed using mated rollers each having a corrugated periphery.

When the blank has been corrugated, it may then be formed as a rectangular tube shown in the end view of Figure 5. Rectangular forming may be accomplished by first producing right angle bends in the blank with suitable tools at the location of the corners of the tube and thereafter lapping and soldering the seam. Other seaming techniques such as welding or brazing be substituted for soldering, or the oint may be partially seamed sufficiently only to permit molding of the sheathing 31 thereover; in which case a limited amount of twisting will be permitted in the guide. Furthermore, a butt joint may be substituted for a lapped joint. Automatic machinery to combine the operations may be employed, wherein the blank is given transverse corrugations and immediately thereafter the corner radii are produced, all in one pass through a suitable forming device.

I locate the seam of my flexible wave guide at the center of the broad inner face since, at this location, the current travels parallel to the seam whereas, if the seam were located at any other position where the current travels either vertically or horizontally of the guide, the seam could be a potential source of electrical losses. The construction of the seam is such that, there is a minimum of surface discontinuity on the inside, the lap being offset outwardly of the guide as shown in the drawing.

One arrangement for associating the flexible guide with a fitting is to gradually decrease the depth of the corrugation as shown at 32 in the right hand end of the composite guide, the material of the guide having non-corrugated characteristics 33 at the intersection with the fitting 3D. A guide of this description may be sweatedon to the fitting by soldering procedures and given a finished termination at the outside face of the fitting, wherein there will be no objectionable refiections in the transmission of high frequency current.

If the tapered or decreasing corrugation construction is to be followed, the side elevation of the right hand end of the blank 35 will appear as shown in the enlarged view in Figure 6. This transformation from corrugated section to noncorrugated may take place over several corrugations as shown, each in decreasing depth, or, if desirable, the transformation may go directly from the full depth corrugation to the non-corrugated form.

There are still other alternatives possible in the mode of transforming the material of the guide from flexible corrugated side wall construction to rigid non-corrugated side wall construction. For instance, instead of retaining a constant corrugation pitch and gradually decreasing the height, as shown in Figure 6, the pitch may be increased and the corrugation height decreased until the non-corrugated section is reached. Likewise, the pitch and the depth may both be decreased until the noncorrugated section is reached, in fact, any gradual and uniform change will be satisfactory. The mechanical characteristics will dictate to some extent the choice of transformation, it being advantageous to distribute the bending of the guide away from the fitting to which it is attached to avoid sharp bending.

As a further alternative the gradual transformation from full corrugation to no corrugation may be replaced with a horn type transformation as shown in Figure 7. In this construction the change takes place according to horn design from the low extremity of a corrugation to the inside dimension of the rigid section as at 32, or, conversely, the horn may be of a reverse taper from the top of the convolution to the effective guide dimension.

On the left hand end of composite guide the flexible corrugated section extends entirely through fitting 29 and may be soldered thereto as by the use of soft solder 34 which adheres to the inner wall of the fitting and fills in between the corrugations of innercore 28 and the fitting. A preferable termination of this sort would be one where the tube is severed in a manner as shown which will present the least amount of reflecting surface, although it is not always pos sible in practice to make a severance of this description.

My invention as described above is provided particularly for use where one may require flexibility in a wave guide and at the same time provide for standard wave guide application technique. It is to be understood that changes may be made in the mode of use of the improved technique described, for instance, the transformation from flexible corrugated to non-flexible non-corrugated section may be desired at locations other than at the end of the guide. Furthermore, it may be desirable to have a rigid section which is intermediate of flexible sections wherein the technique of my invention will also be applicable. Size and thickness of material used to make a wave guide are obviously dependent upon the particular application at hand and upon the characteristics of the kind of material used. While I have indicated the application to ultra-high frequency, it is considered that wave guides according to my invention may be used for waves of all frequencies which are adapted to hollow guide transmission.

Iclaim:

1. In a flexible wave guide constructed in the form of a hollow tube and adapted to the efiicient propagation therethrough of ultra-high frequency Wave energy, in combination, a corrugated section to permit bending of the guide, a non-corrugated section of equivalent electrical size with respect to the corrugated section for the attachment of fittings or the like, and an intermediate section extending from the corrugated to the non-corrugated sections consisting of stepped corrugations.

2. In a flexible wave guide constructed in the form of a hollow tube and adapted to the efficient propagation therethrough of ultra-high frequency wave energy, in combination, a corrugated section to permit bending of the guide. a non-corrugated section of equivalent electrical size with respect to the corrugated section for the attachment of fittings or the like, and an intermediate section extending from the corrugated to the non-corrugated sections consisting of a group of stepped corrugations, the adjacent stepped corrugations having increased corrugation pitch.

3. In a flexible wave guide constructed in the form of a hollow tube and adapted to the efiicient propagation therethrough of ultra-high frequency wave energy, in combination, a corrugated section to permit bending of the guide,

a non-corrugated section of equivalent electrical size with respect to the corrugated section for the attachment of fittings or the like, and an intermediate section extending from the corrugated to the non-corrugated section consisting of adjacent corrugations of diminished depth and diminished pitch.

JOHN M. LAMB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Wave Guide Junctions and Terminations, from the magazine Radio, July 1944 (pages 24 and 25 in particular). 178-44.1D.

Introduction to Flexible Waveguides," from the C. Q. magazine, 1. e., The Radio Amateurs Journal, November 1946 (pages 25-27). 178- 44.1D. 

